In a CO2 laser, a discharge is maintained in a gaseous gain medium including CO2. The discharge may be maintained by applying either a radio frequency (RF) or a continuous (DC) high voltage to the gain medium. Prior CO2 lasers include a laser type generally referred to as a folded-waveguide laser. In a folded-waveguide laser, a ceramic block includes a plurality of waveguide channels arranged at an angle to each other to form the folded waveguide. The gaseous gain medium fills the waveguide and the discharge is maintained by applying the high voltage across parallel electrodes on either side of the block. A laser resonator including two end mirrors and one or more folding mirrors has a folded-resonator axis extending through the folded waveguide. Examples of folded waveguide lasers are described in U.S. Pat. No. 6,192,061.
In the folded-waveguide laser, before the discharge can be maintained in the gain-medium, it must be initiated (ignited) in some way. One commonly practiced method of discharge ignition is to apply a higher voltage to the gain medium than is required to maintain the discharge, and then reduce the applied voltage to a level that will maintain the discharge. This ignition method requires a high voltage power supply capable of initially applying a high voltage pulse or series of pulses to the gain medium to ignite the discharge, and capable of operating at the reduced voltage to maintain the discharge. Typically, pulses having a peak voltage at least twice that of the RF voltage are required. Another possible method of igniting the discharge is to utilize a glow-plug device or a spark-plug device. Either of these methods can require one or more power supplies involving electronic circuitry that is more complicated and expensive than would be required simply to provide that voltage necessary to maintain the discharge. The inclusion of the additional circuitry in the RF power supply for generating the higher voltage ignition RF pulses adds complexity and cost. It would thus be advantageous to eliminate the need for the high peak power RF pulses to ignite the discharge.